When the conductors in a flat conductor cable must be disengageably connected to conductors on a circuit board, it is common practice to use electrical connectors of a type comprising an insulating housing having contact terminals therein which are soldered to the conductors on the circuit board. The housing and the contact terminals are arranged such that the end of the flat conductor cable can be inserted into the housing and upon insertion, the conductors of the cable will be electrically contacted by the contact terminals. Other types of connectors for connecting flat conductor cable conductors to conductors on a circuit board are also known and most of them consist of an insulating housing containing contact terminals which conduct current from the cable conductors to the circuit board conductors.
It is also known to use devices such as connector clip to connect conductors of a flat conductor cable to conductors on a circuit board. Devices of this type are disclosed in U.S. Pat. Nos. 4,169,641; 4,172,626; 4,181,386; and 4,252,389.
U.S. Pat No. 4,169,641 discloses a connector clip device for connecting the conductors of a flat conductor cable to conductors on a circuit board comprised of a single one-piece stamped and formed device which holds the cable conductors directly against the circuit board conductors. The connector is a flat clip member having parallel spaced-apart coplanar support strips and a clip bar which extends between the support strips in a plane which is offset from the plane of the support strips. A plurality of cantilever springs extend from the clip bar obliquely towards and past the plane of the support strips. The connector clip is mounted on the circuit board in straddling relationship to the circuit board conductors with the cantilever springs in alignment with the circuit board conductors. The end of the flat conductor cable is inserted beneath the clip bar and pushed parallel to the springs and the support strips until the cable is beneath the free ends of the springs and the cable conductors are against the circuit board conductors. The springs bear against the insulated top surface of the cable so that the circuit board conductors and the cable conductors are pressed against each other to establish electrical contact. The clip does not carry an electrical current but merely clamps the conductors together.
U.S. Pat. No. 4,172,626 discloses and claims a one-piece stamped and formed connector clip which is adapted to be mounted on a circuit board in straddling relationship to a plurality of parallel side-by-side conductors on the circuit board. The clip serves to connect conductors on a thin film to the circuit board. The clip has a plurality of cantilever springs extending from one of its edges which bear resiliently against the circuit board conductors when the clip is mounted on the circuit board. The clip does not carry an electrical current but merely clamps the film conductors against the circuit board conductors. The conductors on the film are disengageably connected to the circuit board conductors by simply inserting a portion of the film between the spring members of the clip and the surface of the board so that the springs serve to clamp the film conductors against the circuit board conductors. Connector clips also can be used to connect cable conductors to terminal posts extending from a board or to flat conductors on the surface of the circuit board.
Connector clips of the types disclosed in the two patents discussed above can be used successfully and to advantage when the film is comparatively strong and firm and the conductors are durable and resistant to damage from abrasion. Thus, clips as described in the above patents can be used for example where the film is relatively heavy such as a polyester film and the conductors are of wrought copper conductors bonded to the film.
Difficulties are encountered when it is attempted to use such a connector clip with extremely thin films having fragile conductors on their surface. The thin films tend to buckle when an attempt is made to insert them between the springs of the connector slip and the surface of the circuit board against which the springs are biased. The fragile conductors such as printed conductors and screened conductors, which are widely used on extremely thin films are, furthermore, damaged during insertion of the film for the reason that they cannot withstand the abrasive effects of the springs as they are inserted between the connector clip and the surface of the circuit board.
U.S. Pat. Nos. 4,181,386 and 4,252,389 disclose connector clips having zero insertion force characteristics, that is an arrangement whereby the film can be inserted when the contact springs are spaced from the conductors on the surface of the circuit board so that no compressive forces are imposed on the film or on the conductors during insertion.
The connector clip disclosed and claimed in U.S. Pat. No. 4,181,386 is comprised of a rectangular clip bar having spaced-apart cantilever springs extending from one of its side edges. These springs are reversely bent adjacent to the one side edge and extend from the bent portion diagonally towards the conductors on the surface of the circuit board. Each spring is resiliently biased against a conductor when the clip is mounted on the circuit board so that a cable or film can be inserted between the springs and the surface of the circuit board and the springs will press the film conductors against the circuit board conductors. The zero insertion force feature is achieved by providing the free ends of the spring members with tool-engageable portions and constructing the clip for cooperation with a tool which is uniquely suited to engage the free ends of the springs and raise them from the surface of the circuit board during insertion of the film.
The device disclosed and claimed in U.S. Pat. No. 4,252,389 is of the general class described in U.S. Pat. No. 4,181,386. The zero insertion force feature is achieved, however, by providing an integral unloading means for the springs that does not require the use of a specialized tool. The clip is comprised of a one-piece stamped and formed member having a clip bar and having cantilever springs extending from one side edge of the clip bar. The springs are reversely bent and have spring arm portions which extend towards, and are resiliently biased against, the circuit board conductors when the clip is mounted on the circuit board, the contact areas being beneath the clip bar. Each spring has an end portion which extends from the contact area diagonally away from the surface of the circuit board and beyond the other side edge of the clip bar. A lifting bar is provided at the ends of the springs so that the springs can be raised from the surface of the circuit board by merely moving the lifting bar away from the surface of the circuit board.